An International Symposium on the Brattleboro Rat will be held at Dartmouth Medical School on September 5-7, 1981. Over the years, it has become apparent that Brattleboro rats have a number of abnormalities in addition to diabetes insipidus. Examples include: stunted growth; relative infertility; deficiencies of hypothalamic releasing factors; disorders of memory and behavior; altered sensitivity of target organs, such as the kidney, brain, and uterus, to vasopressin and other hormones; lack of neuropeptides other than vasopressin; lack of nephron heterogeneity; high plasma levels of renin and angiotensin but not of aldosterone; altered production of renal prostaglandins; hypokalemia; altered circadian rhythms; and many others. These additional abnormalities -- all probably due to the single, discrete absence of vasopressin -- contribute to the total biology of the Brattleboro rat, which must be taken into account as results obtained with this experimental model are interpreted. It is therefore the main purpose of the Symposium to describe as fully as possible the biology of this rat and to relate that biology to the absence of vasopressin. Accordingly, the program covers the status of the following systems in Brattleboro rats: (1) reproduction and development; (2) neurohypophysical principles; (3) water balance; (4) electrolyte balance; (5) endocrinopathies other than diabetes insipidus; and (6) behavior and central nervous system. The conference will be held on the campus of Dartmouth College and Dartmouth Medical School. The timing of the conference, between semesters, enables us to offer to participants the extensive dormitory, dining, athletic, and cultural facilities of this university at much lower cost than if commercial resources had to be used. The proceedings of the symposium will be published. The volume will include, in addition to a report of the lectures, discussions, and posters, such practical matters as a suggested nomenclature, recommendations for breeding and of mode and dosage of replacement therapy with vasopressin, as well as a complete bibliography on the Brattleboro rat. It is hoped, therefore, that the publication will serve not only as a resume of the deliberations of the conference but also as a handbook that will be useful for future work with these animals.